Modeling Long-Time and Macroscopic Behavior of Complex Atomistic Systems with Application to Silicon-based Lithium Batteries

在许多应用领域，系统的行为敏感地依赖于属于原子尺度的性质，即，埃和飞秒尺度。然而，感兴趣的性质和行为通常是宏观的，发生在厘米到米的尺度上，并且以分钟到年的尺度上的缓慢演变为特征。目前还没有一种计算上易于处理的基于原子的模型来研究这种在几分钟到几年的时间尺度上和宏观样品中的缓慢现象，同时保持对材料的严格原子描述。该项目解决了预测科学中的这一长期差距。这种方法提供了前所未有的能力，在原子尺度上的缓慢，耦合，热机械化学过程介导的器件级性能的研究。因此，除了锂离子电池的这种应用之外，这种方法可以预期作为在需要仔细考虑原子级过程同时阐明长时间尺度上的宏观性质的应用中的使能工具具有深远的影响，例如，合金和辐照材料的稳定性、互连中的电迁移、腐蚀和环境辅助开裂等。本项目所发展的经验原子动力学模型、变分平均场近似方案、变分时间离散算法和空间粗粒化方案将被应用于一个经过验证和验证的高性能计算求解器--扩展准连续体（XQC）求解器，并在社区中广泛传播。它结合了非平衡统计力学、动力学和近似理论的要素。这种方法提供了前所未有的能力，在原子尺度上的缓慢，耦合，热机械化学过程介导的复杂的多物种原子系统的长期宏观行为的研究。被认为是在散装和纳米线（SiNW）的硅锂化的调查的新方法的应用。硅在锂离子电池中作为高能量密度阳极材料的潜在用途受到锂化过程中发生的大量机械降解的阻碍。目前，仅用于汽车应用的这种存储的全球市场规模估计为15亿美元，预计到本世纪末将增长3,000%以上。在器件级和大量充电/放电循环中预测性地模拟硅锂化的能力预计将能够识别和评估用于锂电池应用的新型纳米工程材料。

In a number of areas of application, the behavior of systems depends sensitively on properties that pertain to the atomistic scale, i.e., the angstrom and femtosecond scales. However, often the properties and behaviors of interest are macroscopic and take place on the scale of centimeters to meters, and are characterized by slow evolution on the scale of minutes to years. No computationally-tractable atomistically-based models appear to be as yet available to study such slow phenomena over time scales of the order of minutes to years and in macroscopic samples while maintaining a strictly atomistic description of the material. This project addresses this chronic gap in predictive science. This approach offers unprecedented capability for the study of device-level properties mediated by slow, coupled, thermal-mechanical-chemical processes at the atomistic scale. Thus, beyond this application to Li-ion batteries, this methodology may be expected to have far-reaching impact as an enabling tool in applications requiring the careful accounting of atomic-level processes simultaneously with the elucidation of macroscopic properties over long time scales, e.g., stability of alloys and irradiated materials, electromigration in interconnects, corrosion and environmentally-assisted cracking, among others. The empirical atomic-level kinetic models, variational meanfield approximation schemes, variational time-discretization algorithms and spatial coarse-graining schemes developed under the project will be implemented into a verified and validated high-performance computing solver, the Extended Quasicontinuum (XQC) solver, for broad dissemination in the community.This work is concerned with the further development and implementation of a novel multiscale analysis methodology. It combines elements of non-equilibrium statistical mechanics and kinetic and approximation theory. This approach offers unprecedented capability for the study of the long-term macroscopic behavior of complex multi-species atomistic systems mediated by slow, coupled, thermal-mechanical-chemical processes at atomistic scales. Application of the novel methodology to the investigation of silicon lithiation, both in bulk and in nanowires (SiNW) is considered. The potential use of silicon as a high energy-density anode material in Li-ion based batteries is hampered by the extensive mechanical degradation that occurs during lithiation. The current global market size for such storage, just for vehicle applications, is estimated at $1.5 billion, and is expected to grow to by more than 3,000% by the end of the decade. The ability to simulate silicon lithiation predictively at the device level and over large numbers of charge/discharge cycles is expected to enable the identification and assessment of novel nano-engineered materials for Li battery applications.